Candida albicans, and opportunistic yeast, normally present in the mouth as a harmless member of the microbial flora, is the most frequently encountered and most important fungal pathogen in the oral cavity. In HIV infected individuals, acquisition of oral candidiasis has become an early indicator of the development of opportunistic infections and AIDS. At present, little is known about the shift from C. albicans commensalism to parasitism. An understanding of this shift form the normal to the diseased state in relation to the regulation of C. albicans in the oral cavity by nonimmune natural host defense factors represents the long term goal of this research. Our specific aims will focus upon the family of the salivary histidine-rich polypeptides (HRPs) which are thought by us to be the natural antifungal agents of the mouth. Both in vitro and in vivo studies will be used to accomplish the following: 1) Determine the structures of each of the six major HRPs. Purification and characterization of the HRPs from parotid saliva will be achieved by HPLC, followed by amino acid gas phase sequencing. Structures will be confirmed through comparison to chemically synthesized peptides. 2) Determine the structures of the minor breakdown peptides of these six major HRPs. The specificity of parotid salivary proteolytic enzymes will be assessed through cationic polyacrylamide gen electrophoresis, HPLC analysis and amino acid sequencing. 3) Determine the concentration of the major and minor HRPs in the parotid salivas of normal healthy individuals. HPLC and immuno-assays will be used to quantitate the HRPs. 4) Determine the antifungal potency of physiological concentrations of the HRPs and parotid saliva against C. albicans. Antimicrobial susceptibility testing will include both blastospore colony forming unit viability and germ tube development assays. 5) Determine whether the HRPs can kill C. albicans and other yeast species growing on the denture acrylic surface. A clinical model system employing denture stomatitis patients has been developed from testing the antifungal effects of the HRPs at the in vivo level. 6) Determine the relationship between AIDS, oral candidiasis and the HRPs. Parotid salivas of HIV-infected individual with and without oral candidiasis will be analyzed for the HRPs and for antifungal potency. It is hypothesized that the prevention of oral candidiasis may lead to the prevention of the development of opportunistic infections and AIDS.